The present invention relates to information recording methods and apparatuses which use a medium for recording information by irradiating an energy beam and more particularly, to an information recording method and medium which can exhibit excellent effects on a phase transition optical disk as well as to an information recording apparatus based on the information recording method.
In a related art method for performing recording and erasing operations over a rewritable recording film, for example, when an optical disk is used which has an exchange coupling two-layer film as a recording film as disclosed in U.S. Pat. No. 5,475,657, or when a phase transition type optical disk recording film is used which can erase information at high speed by realizing crystallization in substantially the same time as a laser irradiation time for recording as disclosed in JP-A-62259229 (laid-open on Nov. 11, 1987); the recording and erasing are carried out by changing energy of one energy beam to one of at least two levels higher than a reading power level, that is, by changing the energy of the energy beam to one of at least a high power level and an intermediate power level. This method is advantageous in that so-called overwriting (rewriting based on overwriting) of recording new information while erasing existing information can be realized. Further, as disclosed in JP-A-62259229 and JP-A-3-185629 (laid-open on Aug. 13, 1991), such a phenomenon that a recording mark becomes a tear drop shape can be suppressed (a backward width of the recording mark becomes larger than a forward width thereof) by changing the energy of an energy beam into one of three power levels, that is, high and intermediate levels and a level lower than the intermediate level.
In recent years, there has been put in practical use a DVD-RAM (digital video disk-random access memory) which uses a 120 mm-diametered disk made of phase transition material and having a memory capacity of 2.6 GB on its one side. A recording control method employed in this example is as shown in FIG. 1 and is explained as DVD Specification for Rewritable Disc (DVD-RAM), Part 1, Physical Specifications, version 1.0 (July, 1997), Page PHX-9, FIG. 1.
JP-A-63-48617 (laid-open on Mar. 1, 1988) also discloses a method for changing an energy beam depending on a mark length (corresponding to a region length in a second state in claims at the time of its application) or on a space length (corresponding to a region length in a first state in claims at the time of its application).
Also disclosed in JP-A-8-287465 (laid-open on Nov. 1, 1996) is a method for converting an energy beam to a multi-pulsed train depending on a mark length or a space length.
Studies concerning achievement of a higher density of rewritable digital video disk (DVD-RAM) using a phase transition recording film have recently been advanced. With such an optical disk device as to perform mark edge recording over a phase transition recording film as in DVD-RAM, it is required for the purpose of avoiding mark shape distortion or missing of erasing recorded marks that an achieved temperature and a cooling rate in a record mode are substantially the same even in any outer edge of a region of a recording film melted for formation of a recording mark. However, methods proposed so far failed to satisfy the above condition sufficiently in their various recording waveforms and were limited in their achievable recording densities. Further, recording characteristics of information recording medium usually vary with medium manufacturers, manufacturing times and lots. Thus as it is desired to obtain higher density recording, it becomes more difficult to secure a recording compatibility therebetween.
In particular, in the case of a DVD-RAM having a recording capacity of 4.7 GB higher in density than a DVD-RAM having a recording capacity of 2.6 GB, when recording is carried out with the same spot diameter as in the 2.6 GB DVD-RAM, compatibility with the 2.6 GB DVD-RAM can be achieved more easily. However, as a linear density is increased with the same spot used, a spacing between positions at which two adjacent recording pulses are irradiated on the recording medium becomes smaller than the spot diameter of a laser beam on the medium. Therefore, since light distribution is overlapped when compared with the 2.6 GB case, it becomes necessary to prevent distortion of a recording mark shape caused by the overlapping. Moreover, when a space between recording marks is small, impossible separation between the marks with a reading beam spot causes a shift of a recording mark edge position of a reproduction signal waveform, it is also required to prevent such a shift. The edge position shifting way depends largely on the design of the recording medium, and the recording waveform suitable for a specific recording medium is not always suitable for another recording medium. In current circumstances, because of the increased linear density, the recording mark edge shift is increased by a mismatch between the recording medium and recording waveform to such a level as not to be negligible.
It is therefore an object of the present invention to provide a method and apparatus which can accurately record information with use of the same spot and can increase its density while attaining a compatibility. A related object of the present invention is to provide an information recording method, medium and apparatus which can stably record information on various sorts of recording media having different characteristics and also can easily secure a recording compatibility therebetween.
In order to attain the above objects, an information recording method, medium and apparatus which follow are used.
1) An information recording method wherein a single recording mark is formed on a recording medium with use of a train of a plurality of energy beam pulses, and any of a first case where a falling edge timing of a head pulse in the energy beam pulse train is substantially stationary while a rising edge timing thereof is varied and a second case where the rising and falling edge timings of the head pulse are varied, is used to record information on the basis of control data previously recorded on the recording medium.
2) An information recording apparatus which comprises an energy beam generator; a power adjustment mechanism for adjusting a power level of an energy beam generated by the energy beam generator; a holder mechanism for holding a recording medium; a movement mechanism for relatively moving the energy beam and the recording medium; a signal processing circuit for changing information to be recorded to the power level of the energy beam; first timing adjustment means for causing the power adjustment mechanism to control the energy beam generator to generate a train of a plurality of energy beam pulses from the generator, for substantially fixing a falling edge timing of a head pulse in the energy beam pulse train, and at the same time for changing a rising edge timing thereof on the basis of control data previously recorded on the recording medium at time of forming a single recording medium on the recording medium; and second timing adjustment means for changing the rising and falling edge timings of the head pulse.
3) An information recording method which includes at least one of methods 1 and 2 and uses a recording medium capable of forming a first state zone with a first power level of an energy beam and a second state zone with a second power level of the energy beam higher than the first power level, wherein the energy beam and the recording medium are relatively moved to irradiate the energy beam on the recording medium and to form the first and second state zones with predetermined lengths and with a predetermined spacing therebetween on the recording medium to record information on the recording medium, a third power level lower than the second power level is provided, and at the time of forming the second state zone having a specific length on the recording medium, a duration of the third power level is included as mixed in a duration of the second power level to convert the energy beam to a multi-pulsed train and to irradiate the energy beam on the recording medium, the method 1 substantially fixes a falling edge position of a head pulse in the multi-pulsed train and moves a rising edge position thereof at the time of forming the second state zone having a specific length, the method 2 substantially fixes a rising edge position of a tail pulse of the multi-pulsed train and moves a falling edge position thereof at the time of forming the second state zone having the specific length, a fourth power level equal to or lower than the first power level is provided, the power level of the energy beam following the tail pulse of the multi-pulsed train is kept at the fourth power level for a predetermined time and then kept at the first power level, and a time during which the fourth power level is kept is always constant regardless of the falling edge position of the tail pulse.
Since the above recording methods set forth in the above 1) and 2), information recording apparatus and corresponding information recording media are employed, the timing adjustment means always suitable for the information recording medium can be selected and information can be recorded therein always stably.
Since the above recording method of the above 3) is used, the time during which the constant fourth power level is maintained can be always realized for the information recording medium regardless of the timing adjustment. Therefore, since thermal conditions always optimum for the information recording medium can be maintained, information can be recorded in the medium always stably.
Explanation will be made as to methods, apparatuses and recording media for recording information always stably in connection with embodiments which follow.